The field of the invention is generally that of extensible or movable conveyor systems for continuously conveying material from a moving receiving location such as a mine face to a relatively fixed discharge location.
In a typical underground coal mining system where the present invention can be used to advantage, three or more parallel rooms may be driven up or retreated simultaneously. A mining machine, either a continuous miner or a loader, follows the advancing or retreating mine face in each room in turn, constantly shifting from one room to another. A fixed floor conveyor such as a panel belt conveyor or room conveyor is generally within a few hundred feet of the mine face and carries the mined coal to a main mine conveyor system or to coal cars, for transfer out of the mine, above ground. The fixed floor conveyor is moved, or extended or shortened, from time to time to keep it within a reasonable distance of the face.
Systems for moving coal from the mining machine to the fixed floor conveyor are either intermittent, or continuous.
The predominant method for moving coal from the face is by shuttle car which is intermittent or discontinuous. It has the basic disadvantage that it does not move the coal continuously, so continuous mining machines operating at the face either have to stop when no shuttle car is present or they require extra equipment such as loading machines or surge cars to store coal between shuttle car trips so the mining machine can operate continuously. Notwithstanding this disadvantage, shuttle cars have offsetting advantages in that they are highly flexible, mobile and adaptable to many different mining plans.
Ever since the beginning of use of substantial numbers of continuous mining machines in the early 1950's, mining machine manufacturers and mining companies have spent a great deal of money and engineering time and talent in trying to develop a conveyor system which would carry coal away from the face continuously as fast as the biggest continuous miner could produce it, and yet be as flexible and adaptable to different mining plans as shuttle cars.
The following four categories represent the concepts for continuous coal transfer that have any significant current use in United States underground coal mines:
A. Bridge conveyor-bridge carrier systems.
B. Extensible belt conveyor systems.
C. Flexible conveyor belt systems.
D. Cascading conveyor systems.
The term "significant current use" does not mean that any large proportion of coal mined is conveyed by these systems. The combined total of all of the operating continuous face haulage systems from the above four categories represents only a very small percentage of the underground coal mining activity in the United States. As pointed out above, the predominant method for moving coal from the face is by shuttle car and probably will remain so until a better continuous system is available. The four categories listed above include the systems that are actually running with some degree of success in mines today, and that are, for the most part, available as production items.
Interest in continuous face haulage is very strong among coal companies, much more so than would be indicated by the number of continuous face haulage systems in use. The relatively few mines that are operating these systems are spending a great deal of effort to make them work effectively. Many companies that do not have continuous face haulage systems in their mines yet are watching the various developments in continuous face haulage with interest.
There is also considerable interest in continuous face haulage among mining machine manufacturing companies. Most of the systems running in mines currently are relatively new designs, although generally they represent concepts that are not new. With the exception of one or two small mining machinery manufacturers, continuous face haulage products do not represent a large portion of overall sales. However, there seems to be a general feeling that the potential market may be substantial if acceptable machinery can be developed.
Because the present invention is a substantial step forward in the development of continuous transfer of coal from a mining machine, each of the above four categories of systems now in actual use will be described briefly.